The medial and lateral menisci are biconcave, generally C-shaped wedges of fibrocartilage interposed between the condyles of the femur and the tibia. Together, the menisci act as crucial stabilizers, providing a mechanism for force distribution, and a lubricant between the tibia and the femur. Without functional menisci, stress concentration occurs in the knee in conjunction with abnormal joint mechanics. These phenomena can result in premature development of arthritis.
The replacement of meniscal tissue with structures consisting of permanent artificial materials, however, is often unsuccessful. This lack of success is due principally to the fact that opposing articular cartilage of human and animal knee joints is fragile. The articular cartilage in the knee joint will not withstand abrasive interfaces, or compliance variances from normal, which eventually result from implanted artificial prosthetic menisci. In addition, joint forces are multiples of body weight that, in the case of the knee and hip, are typically encountered over a million cycles per year. Thus far, permanent artificial menisci have not been composed of materials having natural meniscal properties, nor have they been able to be positioned securely enough to withstand such routine forces.
U.S. Pat. Nos. 6,042,610, 5,735,903, 5,479,033, 5,624,463, 5,306,311, 5,108,438, 5,007,934, and 4,880,429 (each incorporated herein by reference) describe a prosthetic meniscus comprising biocompatible fibers, such as natural polymers, and methods for fabricating such prosthetic menisci. These patents also describe methods of regenerating meniscal tissue by implanting the prosthetic meniscus into a human knee. These patents generally disclose prosthetic menisci formulated from dry, porous matrices of processed natural fibers such as reconstituted cross-linked collagen, which optionally include glycosaminoglycan molecules. Generally, the source of collagen for these prosthetic menisci has been animal Achilles tendons or skin. The reconstitution process removes non-collagenous materials such as glycoproteins, proteoglycans, lipids, native glycosaminoglycans, and the like, which may confer additional elastic properties to the original tissue. However, the reconstitution process can leave antigenic components, causing an immunological reaction when the prosthetic meniscus is implanted into a subject.
Accordingly, there is a continuing need in the art for a substantially immunologically-compatible prosthetic meniscus.